Forty-four bovine viral diarrhoea virus (BVDV) isolates collected from the north of Spain between 1989 and 2000 were characterised at the molecular level. For 24 of these isolates the entire N(pro) gene sequence was determined. Phylogenetic analysis revealed that 21 isolates belong to subgroup BVDV-1b, while two BVDV-1c isolates and one BVDV-1h isolate were found. Furthermore, 20 additional virus isolates were analysed by differential reverse transcription-polymerase chain reaction (RT-PCR) and classified as BVDV-1. The results from our study demonstrate that BVDV-1b is the most prevalent subgroup present in bovine dairy herds of Spain, while there is no evidence for the presence of BVDV-2.